[RFC][Flang][driver] Try to support `flang -cc1as`

[sunshaoce]

Summary

Try to implment using flang -cc1as compile assembly files. Related patch (fc1as): https://reviews.llvm.org/D143478

[kiranchandramohan]

flang/tools/flang-driver/CMakeLists.txt

37–41

In general we are trying to limit or reduce the dependency on Clang. This will further increase the dependency. Can we share more code by moving the common portion to llvm/lib/Frontend?

[clementval]

flang/tools/flang-driver/CMakeLists.txt

37–41

+1

[awarzynski]

If this is all that's needed to have an integrated assembly in LLVM Flang, then this is good news and https://reviews.llvm.org/D143478 should be abandoned in favor of this approach. However, we need to find alternatives to increasing dependency on Clang.

flang/tools/flang-driver/CMakeLists.txt

37–41

+1

[sunshaoce]

Simplified code

flang/tools/flang-driver/CMakeLists.txt

37–41

I think this may need to deal with the TextDiagnosticPrinter part. But I don't have a good way to handle it yet.

[jsjodin]

@sunshaoce, @awarzynski are there remaining issues with this patch? We currently needs this for our testing.

[awarzynski]

In D143572#4192645, @jsjodin wrote:

@sunshaoce, @awarzynski are there remaining issues with this patch?

"However, we need to find alternatives to increasing dependency on Clang." ;-)

We should avoid code duplication, so making sure that flang-new -fc1as == clang -cc1as is a good thing. But the extra dependency on clangFrontend would be a step away from making Flang independent of Clang.

We currently needs this for our testing.

Presumably, this is only needed for compiling assembly files? Why not use clang --cc1as instead? At least as an interim solution.

[kiranchandramohan]

flang/tools/flang-driver/CMakeLists.txt

37–41

@DavidTruby Can you have a quick look whether we can refactor the case for TextDiagnosticPrinter?

[skatrak]

Are there any updates on this patch? We're wondering if an approach has been agreed upon, and whether this is still being worked on or if maybe we can help move this along. Thanks!

flang/test/Driver/asm-code-gen-x86.s

+// Test -emit-obj (X86)
+
+// RUN: %flang -c %s -o - \
+// RUN:  | llvm-objdump -d - | FileCheck %s
+// RUN: %flang_cc1as -triple x86_64-pc-linux-gnu -filetype obj %s -o - \
+// RUN:  | llvm-objdump -d - | FileCheck %s
+
+// CHECK: retq
+
+.globl main
+main:
+  ret

flang/test/lit.cfg.py

 # For now we require '&&' between commands, until they get globally killed and
 # the test runner updated.
 config.test_format = lit.formats.ShTest(not llvm_config.use_lit_shell)
 
 # suffixes: A list of file extensions to treat as test files.
 config.suffixes = ['.c', '.cpp', '.f', '.F', '.ff', '.FOR', '.for', '.f77', '.f90', '.F90',
                    '.ff90', '.f95', '.F95', '.ff95', '.fpp', '.FPP', '.cuf'
                    '.CUF', '.f18', '.F18', '.f03', '.F03', '.f08', '.F08',
-                   '.ll', '.fir', '.mlir']
+                   '.ll', '.fir', '.mlir', '.s', '.S']
 
 config.substitutions.append(('%PATH%', config.environment['PATH']))
 config.substitutions.append(('%llvmshlibdir', config.llvm_shlib_dir))
 config.substitutions.append(('%pluginext', config.llvm_plugin_ext))
 
 llvm_config.use_default_substitutions()
 
 # ask llvm-config about asserts
if config.flang_standalone_build:
     if config.flang_llvm_tools_dir != "":
         config.available_features.add('fir')
         if config.llvm_tools_dir != config.flang_llvm_tools_dir:
             llvm_config.with_environment('PATH', config.flang_llvm_tools_dir, append_path=True)
 
 # For each occurrence of a flang tool name, replace it with the full path to
 # the build directory holding that tool.
 tools = [
-        ToolSubst('%flang', command=FindTool('flang-new'), unresolved='fatal'),
     ToolSubst('%flang_fc1', command=FindTool('flang-new'), extra_args=['-fc1'],
+              unresolved='fatal'),
+    ToolSubst('%flang_cc1as', command=FindTool('flang-new'), extra_args=['-cc1as'],
               unresolved='fatal')]
 
 # Flang has several unimplemented features. TODO messages are used to mark and fail if these
 # features are exercised. TODOs exit with an error in non-assert builds but in assert builds
 # it aborts. To catch aborts, the `--crash` option for the `not` command has to be used.
 if 'asserts' in config.available_features:
     tools.append(ToolSubst('%not_todo_cmd', command=FindTool('not'), extra_args=['--crash'],
         unresolved='fatal'))
 else:

flang/tools/flang-driver/CMakeLists.txt

 # Infrastructure to build flang driver entry point. Flang driver depends on
 # LLVM libraries.
 
 # Set your project compile flags.
 link_directories(${LLVM_LIBRARY_DIR})
 
 set( LLVM_LINK_COMPONENTS
   ${LLVM_TARGETS_TO_BUILD}
   Option
   Support
   TargetParser
 )
 
 add_flang_tool(flang-new
   driver.cpp
   fc1_main.cpp
+  ../../../clang/tools/driver/cc1as_main.cpp
 
   DEPENDS
   # These libraries are used in the linker invocation generated by the driver
   # (i.e. when constructing the linker job). Without them the driver would be
   # unable to generate executables.
   FortranRuntime
   FortranDecimal
   Fortran_main
 )
 
 target_link_libraries(flang-new
   PRIVATE
   flangFrontend
   flangFrontendTool
 )
 
 clang_target_link_libraries(flang-new
   PRIVATE
-  clangDriver
-  clangBasic
+  clangFrontend
 )
 
 option(FLANG_PLUGIN_SUPPORT "Build Flang with plugin support." ON)
 
 # Enable support for plugins, which need access to symbols from flang-new
 if(FLANG_PLUGIN_SUPPORT)
   export_executable_symbols_for_plugins(flang-new)
 endif()
 
 install(TARGETS flang-new DESTINATION "${CMAKE_INSTALL_BINDIR}")

flang/tools/flang-driver/driver.cpp

 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/VirtualFileSystem.h"
 
 using llvm::StringRef;
 
 // main frontend method. Lives inside fc1_main.cpp
 extern int fc1_main(llvm::ArrayRef<const char *> argv, const char *argv0);
 
+extern int cc1as_main(llvm::ArrayRef<const char *> Argv, const char *Argv0,
+                      void *MainAddr);
+
 std::string getExecutablePath(const char *argv0) {
   // This just needs to be some symbol in the binary
   void *p = (void *)(intptr_t)getExecutablePath;
   return llvm::sys::fs::getMainExecutable(argv0, p);
 }
 
 // This lets us create the DiagnosticsEngine with a properly-filled-out
 // DiagnosticOptions instance
createAndPopulateDiagOpts(llvm::ArrayRef<const char *> argv) {
 
   return diagOpts;
 }
 
 static int executeFC1Tool(llvm::SmallVectorImpl<const char *> &argV) {
   llvm::StringRef tool = argV[1];
   if (tool == "-fc1")
     return fc1_main(llvm::ArrayRef(argV).slice(2), argV[0]);
+  if (tool == "-cc1as")
+    return cc1as_main(llvm::ArrayRef(argV).slice(2), argV[0], nullptr);
 
   // Reject unknown tools.
   // ATM it only supports fc1. Any fc1[*] is rejected.
   llvm::errs() << "error: unknown integrated tool '" << tool << "'. "
                << "Valid tools include '-fc1'.\n";
   return 1;
 }
 
int main(int argc, const char **argv) {
   llvm::BumpPtrAllocator a;
   llvm::StringSaver saver(a);
   ExpandResponseFiles(saver, args);
 
   // Check if flang-new is in the frontend mode
   auto firstArg = std::find_if(args.begin() + 1, args.end(),
                                [](const char *a) { return a != nullptr; });
   if (firstArg != args.end()) {
+    // Call flang -cc1as frontend
+    if (llvm::StringRef(args[1]).startswith("-cc1as")) {
+      return executeFC1Tool(args);
+    }
     if (llvm::StringRef(args[1]).startswith("-cc1")) {
       llvm::errs() << "error: unknown integrated tool '" << args[1] << "'. "
                    << "Valid tools include '-fc1'.\n";
       return 1;
     }
     // Call flang-new frontend
     if (llvm::StringRef(args[1]).startswith("-fc1")) {
       return executeFC1Tool(args);